In both cases, with feedback and without, the output devices see the same drive voltage. In the feedback case, however, the common cathode resistor sees not the 2 volts of signal, but 38 volts. This huge increase results in a huge imbalance in drive signals, which the feedback must work to eliminate.
     The feedback must compensate for its use in this circuit, which means that the feedback cannot give its all to extending bandwidth or lowering noise. Remember having 40 dB of feedback is like having $40,000 in the bank: you can buy a BMW or a high-end sound system or a diamond necklace, but not all of them at once. So it is with feedback, it gets used up.
     One solution is not to tie the second grid to the output and use global feedback that terminates into the first stage, usually a grounded-cathode amplifier's cathode. An alternative is to use the differential, gain realizing circuit instead. This topology demanded the use of a constant current source for power supply noise elimination and the current source would also serve to eliminate the unbalanced drive signals. The circuit below illustrates the similar drive signals, but what cannot be seen is the gain imbalance elimination.
     

Feedback and Gain Imbalance
    If a constant current source is not used, the imbalance can be partially corrected through the use of a feedback loop. This is the lazy engineer's answer to virtually any problem: noise, limited bandwidth, high output impedance, and distortion. Design the sloppiest, cheapest circuit you want, no worry, the feedback will take care of it. Imagine if a politician  were to argue that every social ill had one remedy: more laws and more police, one cop in each business, school, playground, church, home, and bedroom, if need be. Sad to say, but it does not require much effort to imagine such a fool.

    Here we have an interesting example of how a feedback loop can exacerbate a problem. In the usual arrangement of the long-tail phase splitter, the second grid goes to ground. If instead it were to connect to the output of the totem pole output stage, then a feedback loop is created. The total gain of the circuit falls bellow unity, the output impedance decreases, and the distortion lessens, but not as much we might expect. Because of the 100% feedback ratio, a much bigger input signal is needed to bring the output stage to full output. This means that rather than 4 volts of input signal, 40 volts of signal might be needed to drive a tube output stage to 36 volts of output signal.

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